The present invention relates to a method of installing a mount assembly in a cathode ray tube. Such is the method that an electron gun structure (hereinafter simply referred to as an electron gun) is sealed to a tube of a cathode ray tube (hereinafter abbreviated to CRT) by measuring precisely a position of the electron gun with respect to a phosphor screen of the CRT so as to set it properly at a predetermined position.
Generally, in the process of manufacturing a color CRT, the phosphor screen, a graphite electrode and a shadow mask are provided in a glass bulb. Subsequently, a stem structure mounted with the electron gun is sealed to an opening end of a glass bulb neck portion. In this case, three streaks of electron beams which contribute to generation of color-signals of red, green and blue are brought to focus upon a preset position on the phosphor screen of the glass bulb. The following constituent elements are requisite to enhancement of convergence characteristics of the color CRT.
Namely, it is required that a level difference (hereinafter referred to as a sealing length) between a standard level (for instance, a level of a reference line of the glass bulb which will be mentioned later) of the glass bulb of the CRT and the standard level (for example, a level of a third grid of the electron gun which will be stated later) of the electron gun has a previously prescribed length.
Precisely speaking, the level difference between the standard level of the glass bulb and the standard level of the electron gun involves a length of interval between the above-described two standard levels when a tube-axis of the glass bulb and an axis of ordinate of the electron gun are arranged to be in the same direction.
A sealing apparatus shown in FIG. 1 has heretofore been employed in such a installing method that the electron gun is so sealed to the glass bulb of the color CRT of this type as to be joined to each other. In the FIG. 1, the reference numeral 1 stands for the glass bulb, 2 represents a bulb holder, 3 designates a pannel holder, 4 denotes a saddle, 9 represents a mount pin, 10 stands for the electron gun, and 11 designates the stem structure. The bulb holder 2 is mounted with the glass bulb 1 which is fixedly retained by the saddle 4 and the pannel holder 3. In a state wherein the electron gun 10 is retained by the stem structure 11, this stem structure 11 is inserted in the mount pin 9; and the mount pin 9 whereby the electron gun 10 and the stem structure 11 are retained is raised by driving means (not illustrated), thereby inserting the electron gun 10 into a neck portion 1b of the bulb 1. Thereafter, the level of the mount pin 9 continues to be adjusted until a dimension measured from a reference line R/L (an imaginary line depicted by a one-dot chain line in FIG. 1) of the glass bulb 1, which line is in general determined by an installing position of the saddle 4, to the standard level of the mount pin 9 is to a predetermined valve. When the predetermined dimension is obtained, the stem structure 11 and the bulb neck portion 1b are subjected to heat-processing, thus sealing the two members.
According to the above-described installing method, fluctuations occur in dimension between the standard level of the electron gun 10 and the standard level (in this case, the reference line R/L) of the glass bulb 1 due to the fact that the dimension at the sealing time which extends from the electron gun 10 to the stem structure 11 fluctuates, and that the stem structure 11 is slackened from the mount pin 9 by mechanical vibrations or other factors, which results in deterioration of the convergence characteristics. It is therefore difficult to procure the CRT invested with desired properties.
Excepting the reference line R/L, for instance, an apical face (or an apex) of an outer surface of the panel 1a, or the apical face (or the apex) of an inner surface of the same panel 1a serves as the standard level of the aforementioned bulb.
The prior art relative to the sealing process of the glass bulb and the electron gun in the CRT is disclosed in the specification of, for example, U.S. Pat. No. 3,962,764.